Scots pine responses to number and density of inoculation points with Leptographium wingfieldii Morelet, a bark beetle-associated fungus

Croisé, Luc; Lieutier, François; Dreyer, Erwin

doi:10.1051/forest:19980408

Cited by 20 publications

(15 citation statements)

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“…In such artificial mass inoculations, fungal cultures have generally been introduced at the cambium level, in holes previously bored with a puncher. As tree death is generally thought to result from disruption of water transport in the sapwood, tree death caused by fungal mass inoculations has been estimated by the fading of the foliage or, most often, by measuring sapwood occlusion or sapwood invasion by the fungus (percentage of occluded or blue stained sapwood in transversal bole sections), after harvesting the trees a few months after inoculations 1985b;Christiansen et al, 1987;Croisé et al, 1998a;Solheim et al, 1993, among others). In some cases, tree death 801p5 Ann.…”

Section: Definition and Quantification Of Beetle Aggressiveness And Fmentioning

confidence: 99%

Stimulation of tree defenses by Ophiostomatoid fungi can explain attack success of bark beetles on conifers

2009

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Keywords:pathogen / forest tree / physiological stress / blue stain fungi / host resistance Abstract • Our aim is to present why the hypothesis, that Ophiostomatoid fungi play an important role in the establishment of most bark beetle species on living conifers, is valuable.• After summarizing knowledge about the relationships of bark beetles with conifers and fungi, we conclude that controversy results from misinterpretations when using fungal pathogenicity to demonstrate the role of Ophiostomatoid fungi in beetle establishment on host trees.• We demonstrate that fungal pathogenicity is not the right parameter to appreciate the role of fungus in beetle establishment on host trees. We argue that artificial low density inoculations that allow the appreciation of fungus ability to stimulate tree defenses and thus to help beetles in overcoming tree resistance must be used in complement to mass inoculations. In both cases, results must be expressed in terms of tree defense stimulation rather than in terms of tree killing.(i) Fungal species stimulating tree defenses are generally not those that grow the best in the sapwood.(ii) We argue that beetle development in the phloem, fungal invasion of the sapwood and phloem, and tree death, occur after tree defenses are exhausted, and that any fungus present in the beetle gallery could thus potentially invade the sapwood after defense exhaustion.• We conclude that stimulation of the tree defense reactions in both the phloem and the superficial sapwood is a real benefit brought by fungi to the beetles during the first phase of establishment (overcoming tree resistance).• Considering the origin of the bark beetle fungus associations attacking living trees and their general functioning based on stimulation of tree defenses, we develop three hypotheses:(i) any beetle species would be helped in its establishment in a given tree species by developing an association, even loosely, with a fungus species belonging to the Ophiostomatoid flora of that tree species; (ii) the necessity of a considerably low level of tree resistance for fungus extension into the tree is the selection pressure that has led fungi to develop their intrinsic ability to stimulate tree defenses, through their ability to grow into the phloem. This association can be completed by antagonistic fungal species controlling extension of the previous fungal species in the tree tissues; (iii) Beetle species using the strategy of overcoming tree resistance are associated with a fungal complex, of which species could assume three roles regarding relationships between beetles and trees: 1-to stimulate tree defenses in the phloem and superficial sapwood, 2-to grow into the sapwood after tree resistance is overcome, and 3-to control phloem extension of the first other two categories. Bringing nutrients to the beetle progeny can be a fourth role.• We propose that bark beetle -Ophiostomatoid associations can be categorized, based on associations' frequency and complexity while taking into account beetle aggressiveness. We show...

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Section: Definition and Quantification Of Beetle Aggressiveness And Fmentioning

confidence: 99%

Stimulation of tree defenses by Ophiostomatoid fungi can explain attack success of bark beetles on conifers

2009

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“…The results of the inoculation experiments with fungal associates of T. piniperda indicate that L. wingfieldii and O. minus are able to overcome the defense mechanisms of Scots pine and may kill healthy trees [4,5,30,31,33,34,[51][52][53].…”

Section: Introductionmentioning

confidence: 99%

Fungi associated withTomicus piniperdain Poland and assessment of their virulence using Scots pine seedlings

Jankowiak¹

2006

Ann. For. Sci.

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-The species composition and virulence of fungi associated with Tomicus piniperda were studied at eight locations in Poland. The fungi were isolated from phloem and sapwood samples taken from insect galleries and then identified. The virulence of the most common ophiostomatoid species was evaluated through inoculations using two-year-old Scots pine seedlings. A great diversity of fungi were found associated with T. piniperda, including 4 837 cultures and 67 species. The most important groups of fungi were the ophiostomatoids and moulds, including mainly Penicillium, Trichoderma and Mucor species. Among ophiostomatoid fungi, Ophiostoma minus and O. piceae dominated, with a frequency of occurrence of 32.4 and 11.5% of inspected galleries, respectively. Occasionally isolated species included Leptographium lundbergii, L. procerum, L. wingfieldii, Graphium pycnocephalum and Graphium sp. 'W'. In general, the frequency of the ophiostomatoid species was highly variable among locations. Leptographium wingfieldii and O. minus, were the only species capable of killing whole plants and penetrated deeper into the sapwood than other species (87-100% mortality during the 11 week incubation period). Other fungi, including O. piliferum, O. piceae and L. procerum, were considerably less virulent.

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“…In addition, after contributing to exhaust the resistance of the tree and allowing the success of attacks, the fungi can also contribute to kill the tree by invading and occluding the sapwood [14,24]. Artificial mass inoculations of bark beetle associated blue stain fungi are often used to mimic mass attacks by bark beetles and to define a critical threshold of inoculation density for individual bark beetle / blue stain fungus / host systems [5,7,9,38]. This method is especially useful for comparison of the resistance level of trees with varying vigor levels or to compare the pathogenicity of different fungi.…”

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confidence: 99%

“…However, it has a very good ability to stimulate the tree response after artificial inoculation [16,18,37], which makes it an excellent test organism to study the defense mechanisms of pine. It displays a high level of virulence since it is able to kill healthy Scots pine trees at a low (about 400/m 2 ) density of artificial inoculation within a 1-m wide inoculation belt [5,38]. It has been suggested to play a possible role in killing trees after attacks by T. piniperda have succeeded [13,14].…”

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confidence: 99%

Variations in growth and virulence of Leptographium wingfieldii Morelet, a fungus associated with the bark beetle Tomicus piniperda L.

Lieutier¹,

Yart²,

Ye³

et al. 2004

Ann. For. Sci.

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-Growth and virulence of various isolates of Leptographium wingfieldii Morelet, isolated from Tomicus piniperda L. and galleries initiated by this insect on Scots pine (Pinus sylvestris L.) at different parts of the forest of Orléans, were compared. Six isolates were tested in 1994 and 15 in 1995. The tested parameters included the growth on malt agar at different temperatures, the ability of the fungus to stimulate the hypersensitive reaction in the phloem and to grow into the reaction zone after isolated inoculations of Scots pine trees, as well as fungal virulence to Scots pine after mass inoculations. Significant differences between isolates were observed for all parameters. These differences mainly refer to gradual variations among isolates, even though some isolates were constantly opposed to each other for all or most parameters. No obvious effect of the locality, from where the isolates had been obtained, was detected. The results suggest that the population of L. wingfieldii in the forest of Orléans consists of isolates that possess a high individual variability in growth characteristics and virulence to their host tree. Fungal growth both on malt agar and in the phloem was positively correlated with the length of the reaction zone in the phloem after isolated inoculations and with parameters related to fungal virulence after mass inoculations. Likewise, length of the reaction zone in the phloem was positively correlated to the number of killed trees and the percentage of blue stained sapwood area after mass inoculations. The results are discussed in relation to the possible origin of the variability in fungal growth and virulence, and to practical use of fungal growth on malt agar and in the phloem for screening and comparing the virulence of various isolates within the same blue stain fungal species.Leptographium wingfieldii / Tomicus piniperda / intraspecific variability / growth / virulence / tree defense reaction / temperature / Orléans Résumé -Variabilité de la croissance et de la virulence de Leptographium wingfieldii Morelet, champignon associé au Scolyte Tomicus piniperda L. La croissance et la virulence de divers isolats de Leptographium wingfieldii Morelet, isolés d'adultes de Tomicus piniperda L. et de leurs galeries provenant d'attaques récentes sur des pins sylvestres (Pinus sylvestris L.) dans différentes zones de la forêt d'Orléans, ont été comparées. Six isolats ont été considérés en 1994 et 15 en 1995. Les paramètres testés étaient la vitesse de croissance sur malt agar à diverses températures, la capacité du champignon à stimuler la réaction hypersensible du liber et à croître dans la zone de réaction après inoculations ponctuelles à des pins sylvestres, et sa virulence après inoculations massives sur Pin sylvestre. Des différences significatives entre isolats ont été observées pour tous les paramètres. Elles correspondent essentiellement à des variations graduelles, même si certains isolats étaient constamment opposés les uns aux autres pour tous ou la plupart des paramètres...

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Scots pine responses to number and density of inoculation points with Leptographium wingfieldii Morelet, a bark beetle-associated fungus

Abstract: -The effects of different densities and total distribution of inoculation points with Leptographium wingfieldii, a fungus associated with the bark beetle Tomicus piniperda, were investigated in Scots pine (Pinus sylvestris

Cited by 20 publications

References 19 publications

Stimulation of tree defenses by Ophiostomatoid fungi can explain attack success of bark beetles on conifers

Stimulation of tree defenses by Ophiostomatoid fungi can explain attack success of bark beetles on conifers

Fungi associated withTomicus piniperdain Poland and assessment of their virulence using Scots pine seedlings

Variations in growth and virulence of Leptographium wingfieldii Morelet, a fungus associated with the bark beetle Tomicus piniperda L.

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